The invention relates generally to metamaterial cloaking. In particular, the invention relates to elevation angle correction for extending two-dimensional cloaking via metamaterials towards quasi-three-dimensional cloaking.
Invisibility has fascinated the public even before H. G. Wells wrote The Invisible Man (1881). A. Alù in “On the Quest to Invisibility” available at http://users.ece.utexas.edu/˜aalu/index_htm_files/Alu_TedxAustin_Text_Figs.pdf summarizes the objective and research of metamaterial cloaking of objects for the lay public at his TED Talk.
An ideal electromagnetic cloak would reconstruct an electromagnetic wave on the cloak's exterior as if the cloak, as well as an object within the cloak, were not there, including properties of electromagnetic phase, group velocity, amplitude and propagation direction. Frequency dispersion, often associated with cloak design, prevents reconstruction of the group velocity, and amplitude, so that a perfect cloak across all frequencies cannot exist. This has been noted by F. Monticone and A. Alù in “Invisibility exposed”, Optica 3 7 (2016) available at haps://www.osapublishing.org/optica/abstract.cfm?URI=optica-3-7-718. Nevertheless, cloaks have been shown to reconstruct the phase velocity, and approach reconstructing the amplitude as noted by D. Schurig et al. in “Metamaterial Electromagnetic Cloak at Microwave Frequencies”, Science 314 977 (2006) available at http://www.ece.utah.edu/˜dschurig/Site/Publications_files/977.pdf detailing research on microwave cloaking.
Nathan Landy conducted research on unidirectional metamaterial cloaks for his dissertation and published a paper on the concept with D. R. Smith: “A full-parameter unidirectional metamaterial cloak for microwaves”, Nature Materials 12 25-28 (2013) available for article download at http://search.proquest.com/docview/1284355009?pq-origsite=gscholar on the diamond configuration cloak. This technology has been further pursued in conjunction with sensor arrangements by SensorMetrix in San Diego, Calif. The concept also suffered that the k-vector had to be perpendicular to the central axis of the cloak.
Even though a true cloak is impossible to create, practical benefits accrue for partial cloaking of objects. For example, D. de la Vega in “Mitigation Techniques to Reduce the Impact of Wind Turbines on Radar Services”, Energies 6 2859-2873 (2013) available at http://www.mdpi.com/1996-1073/6/6/2859/pdf describes interference from wind turbines on ground-based radar installations. S. Magnuson in “British Model May Hold Key to Solving Wind Energy, Radar Clutter Problem”, National Defense 95 683 26-27 (2010) also describes signal interference mitigation by electromagnetic cloaking at http://www.nationaldefensemagazine.org/archive/2010/October/Pages/BritishModelMay HoldKeytoSolvingWindEnergy,RadarClutterProblem.aspx?PF=1 because ground radar is often installed at a fixed location. However, to cloak the support pylon of the windmill, a cloak would be needed in which the k-vector could point in planes other than the horizontal.